The inventors' original LetterScreen (LS) system (illustrated in FIG. 1) has been an attractive feature for first-level verification of high security documents, such as passports. In the LS system, as applied to a passport, a portrait of the passport applicant was built up from lines of microtext. The microtext 101 was personalized; to include the applicant's name, document number and/or other personal data. The personalized text lines fill the entire image. There were slight differences in character size and thickness to clearly show the portrait. LetterScreen was the optimal ghost image, and enhanced security because it directly linked the portrait to the owner & document itself. The first generation of LetterScreen was printed along straight horizontal lines.
The second generation of LS was enhanced by using a slight wave in the text lines. The second generation of LS was even more difficult to reproduce than the first generation LS.
The verification of both original LS and second generation of LS was based on the comparison of text in the LetterScreen and the readable personal data, as well as data on the screen, when OCR lines were read. The verification of the document containing the letter screen required the use of a special magnifier. As such, verification was a slow tedious process.